Encased resistor unit



1944' c. M. OSTERHELD 2,360,264

ENCASED RESISTOR UNIT Filed Nov. 2, 1942 2 Sheets-Sheet l INVENTOR.

. CLARK OSffHf/[LD BY a 7 I ATTORNEY Oct. 10, 1944. ci, M. OSTERHELD ENCASED RESISTOR UNIT Filed Nov. 2, 1942 2 Sheets-Sheet 2 w m mm W Y M fi J13 ATTORNEY Patented Oct. 10, 1944 ENCASED RESISTOR UNIT Clark M. Deter-held, Stoughton, Wis., assignmto McGraw Electric Company, Elgin, Ill., a corv pora tion of Delaware Application November 2, 1942, Serial No. 464,206

8 Claims.

My invention relates to electric resistor or heating units and among its objects are the following: to provide an encased or sheathed resistor or heating unit of relatively simple and highly eflicient construction; to provide a resistor or heating unit having a dielectric coating between the resistance conductor and the outer casing that is inorganic, coherent with either the resistor memlcer or the casing member, that is heat-conductlng, high temperature-resisting and is of very small thickness.

Other objects of my invention will either be apparent from a description of several forms embodying my invention or will beset forth in the specification and particularly in the appended claims.

In the drawings,

Figure 1 is a view in perspective of a resistance conductor used in my improved resistor or heating unit, v

Fig. 2 is a view in perspective of the resistor conductor located within an inner sheath or casns.

Fig. 3 is a view of the members shown in Fig. 2 when wound to helical coil shape, I

Fig. 4 is a fragmentary view in perspective, of an assembled heating unit embodying my invention,

Figs. 5, 6 and 7 are views in perspective of a resistor conductor, a sheath to be applied to the conductor and the conductor and sheath assemb y.

Fig. 8 is a view of the elements shown in Fig. 7 when wound to helical coil shape,

Fig. 9 is an end view thereof,

Fig. 10 is a fragmentary view of a heating unit embodying the elements shown in Figs. 5 to 9 inclusive in assembled condition,

Fig. 11 is a fragmentary of insulated conductor,

Fig. 12 is a view in side elevation of a helically coiled member such as shown in Fig. 11,

Fig. 13 is an end view thereof, and,

Fig. 14 is a fragmentary view in perspective of an assembled resistor or heating unit embodying the elements shown in Figs. 11 to 13 inclusive.

Referring to Fig. 1 of the drawings, I have there illustrated a high current-carrying conductor 2| which may be of any suitable or desired material usually used for resistance purposes or for heating unit purposes, such as Nlchrome. I do not, however, desire to be limited thereto and may, for instance, use aluminum or an aluminum alloy as the resistance conductor. I provide a sheath 23 view of another form therearound, which sheath is made of relatively thin metal, preferably aluminum, on which it is possible to produce. an integral inorganic, heatconducting, high temperature-resisting, electricinsulating coating such as is described in Patent No. 1,526,127. Preferably the method may be that in which the initially flat strip 23 is subjected to electrolytic action in a suitable electrolyte, current passing from the cathode to the member 23 as anode to thereby produce on its surface a coating having the above described characteristics and usually called an anodic coating. For illustrative purposes only I may mention that the thickness of the coating may be on the order of .0004" or .001" and one of the characteristics of such a coating is that it is corrosion-resistant as well as electric insulating and that it is possible to reshape the coated plate. The thickness of the strip 23 may be on the order of .015";

Any suitable or desired means of and method for locating the member 23 around the strip 2i in the position shown in Fig. 2 may be employed.

Referring now to Fig. 3 of the drawings, I have there shown the next step in the manufacture of my improved resistor or heating unit which shows that the sheathed resistance member has been coiled into helical shape and while not necessary, I prefer to position the adjacent turns of the sheathed conductor relatively close together since this increases the amount of energy which will be translated into heat in a heating unit of this kind. It is to be noted that the sheathed conductor member is wound fiatwise.

Referring now to Fig. 4, I have there illustrated an outer tubular, preferably metallic casing 25 into which the helically coiled sheathed eonductor or resistance member has been moved. In order to do this it is only necessary that any suitable or desired means for causing additional turning movement of one end of the coiled resistor member relatively to the other end, whereby the outside diameter of the helical coil is temporarily reduced, after which it is a relatively simple mattcr to insert the members 2| and 23 in the tubular casing 25.

Imayhere point out that while not necessary, I may make the outer tubular casing member 25 of aluminum or of some other metal or alloy which will permit of producing on its inner surface the kind of electric-insulating coating hereinbefore described and having all of the other hereinbe fore mentioned characteristics. This is particularly important when a heating unit of this kind is to be subjected to a. relatively high breakdown voltage stress.

. Referring now to Figs. ,5 to 10 inclusive, I have shown in Fig. 5 a resistance conductor 21 which, while shown as of substantially circular shape in cross section, such as ordinary wire, is not limited thereto. Fig. 6 shows a. sheath 29 which may be of very thin aluminum strip having provided thereon an electric-insulating coating of the kind hereinbefore described. The strip 29 is shown as having been bent around the conductor 21, in Fig. 7 of the drawings, and Fig. 8 of the drawings shows the sheathed conductor 21 as having been helically wound on suitable means well known in the art. It is, therefore, evident that the conductor 21 is surrounded over almost its entire periphery by a sheath having an electric-insulating coating on both its surfaces so that when the conductor wound into.

helical form, as shown in Fig. 8, is inserted in an outer casing 25, as shown in Fig. 10, it will be thoroughly insulated therefrom. The same comments as regards the use and effect of radially-outwardly acting spring pressure applies to this form of conductor as well as to the form shown in Figs. 1 to 4 inclusive.

Referring now to Figs. 11 to,14 inclusive, I have there shown another resistance conductor 3! as of circular cross section, such as wire, hiaving wound therearound a relatively thin metallic wire 33, preferably of aluminum, the outer surface of which has been treated as above described to produce thereon the so-called anodic electric-insulating coating and this wire 33 is wound tight as to its adjacent turns so that these will closely engage each other over substantially the entire length of the conductor ill. The resistor member comprising elements 3| and 33 is wound to helical coil shape as shown in Fig. 12 of the drawings, the same comments conductor, is such that the sheaths protectively enclose or surround the conductor, which makes for easier assembly and isno drawback, since the sheathed resistance conductor is positioned within an imperforate outer casing.

While I have not shown any terminal member or means provided for the heating units shown in the drawings, it is to be understood that any suitable or desired terminal or terminal members may be provided but these are not shown since they constitute no part of my present invention.

It is evident from what has been set forth that the sheathed resistance conductor is the main element effective to hold itself within the outer casing and it is to be further understood that the heating unit may be bent or otherwise manipulated to assume any desired shape with reference to an article, a mass or an area of which is to be heated by such electric heating unit.

Various modifications may be made in the system embodying my invention as herein shown and described and all such modifications clearly coming within the scope of the appended claims are to be considered as being covered thereby.

I claim as my invention:

1. An encased resistance unit comprising a tubular outer metallic casing, an inherently reslient helically-woundmetallic sheath member of substantially closed channel shape in lateral section having on its inner surface an integral,

ber comprising the elements 3| and 33 as having been located within an outer tubular casing 25 which, as has already been hereinbefore stated, may be of a metal on the inner surface of which can be produced an anodic coating or a very thin electric-insulating inorganic high temperature-resisting coating of infinitesimal thickness.

I desire to briefly recapitulate the essential elements'constituting my invention which are, an outer casing which is preferably imperforate to permit of its use in any operating condition where it may be required, which casing, however, may have any shape in lateral section. Within such casing, which may or may not have an electric-insulating inorganic "coating on its inner surface, there is located a resistor member which may, for instance, be Nichrome or any other material used for such purposes and which resistor member is so constructed and shaped as to have an inherent radial springiness which permits it to hold itself in the outer casing while at the same time the length of path of the heat flow is very small. I may point out further that the sheath illustrated, for instance, by member 23 or member 29 is very thin and this tends very markedly to reduce the heat storage capacity of the heat storage mass of a resistor or heating unit of the kind embodying my in" vention.

It may be noted that the dimension of the sheaths shown in Figs. 2 and 7, laterally of the electric-insulating, heat-conducting, high temperature-resisting coating and a resistance conductor within the member of substantially channel shape and substantially protectively covered thereby.

2. An encased resistor unit comprising a resistance conductor of substantially helical-coil shape, a metallic sheath member for said conductor, conforming to the shape thereof and in close operative engagement therewith, and having an integral, inorganic, electric-insulating, heat-conducting and high, temperature-resisting coating on that part of its surface engaging said resistance conductor and an outer metallic casing for said conductor and said sheath member, said sheath member having inherent resiliency to cause it to fit tightly in the casing.

3. An encased resistor unit comprising a tubular outer metallic casing and an electrically-insulated resistance conductor member therein, said electrically insulated conductor member comprising a resistance conductor and a metallic sheath member substantially coextensive in length with said conductor, surrounding the latter substantially entirely and having on at least the conductor-engaging surface thereof an integral, inorganic, electric insulating, heat conducting and high temperature-resisting coating, said electrically-insulated conductor having, a helicalcoil shape and having inherent radially-acting spring effect to cause the outer surface of the sheath member to closely operatively engage the inner surface of the casing.

4. An encased resistor unit comprising a tubular metallic outer casing and an electrically-insulated resistance conductor member in said casing, said electrically-insulated conductor member comprising a resistance conductor having an integral, inorganic, heat-conducting, high tempera-=- ture-resi sting, electric-insulating coatingon its outer surface and a metallic sheath therefor extending substantially entirely around the condil-ctor laterally thereof, said sheath and the con" ductor being of substantially helical-coil shape and having inherent, radially outwardly directed spring action to cause close operative heat-transmitting engagement between the outer surface of the sheath and the inner surface of the casing.

5. An encased resistor unit comprising a tubu lar, metallic outer casing and an electrically-insulated resistance conductor member therein, said conductor member comprising a resistance conductor and a metallic sheath therefor extending protectively around the conductor laterally thereof, the outer surface of the conductor and at least the inner conductor-engaging surface of the sheath having thereon an integral, inorganic, high temperature resisting, heat conducting, electric-insulating coating, said conductor member being of substantially helical-coil shape and having an inherent radially-outwardly acting spring effect to hold it in proper operative position in said tubularpasing.

6. An encased resistor unit comprising a tubular, metallic outer casing and an electrically-insulated resistance conductor member therein, said conductor member comprising a resistance conductor and a metallic sheath therefor extending protectively around the conductor laterally thereof, the inner surface of the casing, the outer surface of the conductor and at least the inner conductor-engaging surface of the sheath having thereon an integral, high temperature-resisting, heat-conducting, electric-insulating coating, said conductor member being of substantially helicalcoil shape and having an inherent radially-outwardly acting spring effect to hold it in proper operative position in said tubular casing.

7. An encased resistor unit comprising a tubular outer casing of aluminum and a conductor member therein comprising an aluminum resistance conductor and an aluminum sheath covering substantially the entire outer surface of the resistance conductor, said conductor member being helically coiled with inherent springiness to cause good heat-conducting engagement between the sheath and the casing, the inner surface of the casing, and the entire outer surface of the conductor and of the sheath having thereon an integral, electric-insulating, heat-conducting, high-temperature resisting coating.

8. An encased resistor unit comprising a tubular outer casing of aluminum and a conductor member therein comprising an aluminum resistance conductor and an aluminum sheath, having a thickness on the order of .015", covering substantially the entire outer surface of the resistance conductor, said conductor member being helically coiled with inherent springiness to cause good heat-conducting engagement between the sheath and the casing, the inner surface of the casing, and the entire outer surface of the condu-ctor and of the sheath having thereon an integral, electricinsulating, heat-conducting, hightemperature resisting coating, the thickness of said coating being on the order of .001".

CLARK M. OSTERHELD. 

